A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In scanners, target portions are irradiated in accordance with a certain grid, i.e. a scanner grid. Generally, such a scanner grid is an absolute grid, i.e. the grid points are defined by absolute coordinates, and not for instance by relative distances. During processing of the substrate, during or after exposure, the pattern, and thus the grid, as transferred on the substrate may be distorted. Consequently, if a first pattern is transferred to a first layer n in accordance with the scanner grid, and due to processing of layer n this grid is distorted after transfer, transferring a second pattern towards a next layer, i.e. a second layer n+1 on top of the first layer, by using a similar grid as used to transfer the first pattern may lead to misalignment of the first and second patterns in layers n and n+1 respectively.